1. Field of the Invention
This invention pertains to tubular intraluminal devices (such as stents or catheters) for placement in a lumen of a patient's body. More particularly, this invention pertains to a method for manufacturing such devices.
2. Description of the Prior Art
Intraluminal devices for placement in a lumen of a patient are widely used. For example, stents are commonly used to treat obstructed coronary arteries. Typically, such stents are reticulated tubular structures. The stents are placed on a balloon tip catheter and advanced through the patient's blood vessels to an occluded artery. At the occluded site, the balloon is expanded to enlarge the stent's diameter. With the stent so enlarged, the balloon is deflated and the catheter is removed from the patient leaving the enlarged stent in place with the intent that the formerly occluded site is held patent by the stent.
In addition to advancing stents as described above, catheters are used in a wide variety of applications. Accordingly, catheters are available in a wide variety of designs. Many such designs require extremely small diameter and flexible catheters. For example, in neurological applications, catheters must be extremely narrow and flexible in order to be advanced through the patient's vasculature to a desired site.
To achieve the small diameters and desired flexibility as well as other properties, stent, catheters and other tubular intraluminal devices may include hollow tubes fabricated with a plurality of openings formed through the walls of the tube. For example, U.S. Pat. No. 5,573,520 dated Nov. 12, 1996 teaches a catheter with a tube having a plurality of apertures to increase flexibility.
Since intraluminal devices have such small diameters, it is extremely difficult to fabricate these devices. For example, prior art stents would be formed by laser-machining a solid-walled metal tube. Through accurate control of the laser, the laser would be axially and circumferentially moved relative to the stent and selectively energized to form highly detailed holes through the wall of the tube and, hence, form a stent of desired intricate lattice pattern.
Laser machining is very costly as well as presenting other problems. As a result, the art has developed other techniques for forming reticulated intraluminal devices. For example, U.S. Pat. No. 5,421,955 to Lau et al. dated Jun. 6, 1995 describes a process for forming stents from a hollow metal tube. The tube is coated with a coating resistant to chemical etching. Using a laser, portions of the coating are removed to expose a pattern on the tube corresponding with a pattern of tube material to be removed in a desired stent design. With the coating so removed, the tube is chemically etched to remove tube material exposed by reason of the selective removal of the coating. Subsequent to such etching, the remainder of the coating is removed to finish the stent forming process. Even though the laser is not being used to remove metal, the use of a laser is still required to remove the coating. Such a use is complicated, costly and difficult to control.
Commonly assigned U.S. Pat. No. 5,741,429 issued Apr. 20, 1998 permits the formation of reticulated intraluminal tubular devices such as stents and catheters in a chemical etching process not requiring the use of lasers and their disadvantages. In this patent, a chemical resistant coating is applied to a tube. Using a photo-mask, portions of the coating are exposed to a light source. The exposed portions are removed in a developing process to expose a pattern on the surface of the tube. The tube is then chemically etched to remove tube material exposed through the developed pattern. Following such etching, the remainder of the coating is removed.
While the '429 patent represents a significant advance in the production of stents and catheters, chemical etching presents certain challenges. For example, when a chemical etchant is applied to a limited exposed area on the exterior of a tube, the etchant does not dissolve perfectly radially toward the center of the tube. This tendency precludes certain stent pattern geometries which can be formed in a chemical etching process. For example, intricate, narrow corners are difficult to form in stents and catheters made by chemical etching. Further, the non-radial etching path can result in the formation of stent or catheter walls being non-radial relative to the tube's axis. These non-radial walls intersect with the interior cylindrical surface of the stent tube in such a manner that sharp knife edges can be formed. Such edges are undesirable and require further process.